Available evidence favors the presumption that lipoprotein lipase is significantly involved in tryglyceride removal from the plasma. Research done in our laboratory as well as other laboratories has indicated the presence of at least three triglyceride lipases in the post-heparin plasma. Metabolic and biochemical characterization of these enzymes as well as their functional relationships is expected to provide relevant new knowledge concerning triglyceride removal mechanisms. These studies are a continuation of the research in progress for several years in the Cardiovascular Research Program. Our results suggest that post-heparin plasma contains two distinct lipoprotein lipases, while only one has been demonstrated in milk and adipose tissue. These two lipoprotein lipases have been designated LPLC-I and LPLC-II based on lipoprotein C polypeptide activation. These two lipoprotein lipases have been isolated and purified. Our major efforts are directed towards characterizing them by substrate specificity for triglyceride-rich lipoprotein particles, preparation of specific antibodies, and by conventional protein analytical methods. Similar methods will be utilized to characterize post-heparin plasma LPLC-I and LPLC-II from Type I, III and V hyperlipoproteinemic subjects. Furthermore, simple procedures which can utilize smaller samples of post-heparin plasma are being developed to screen samples of post-heparin plasma for the two lipoprotein lipases and any other triglyceride hydrolase activities.